The present invention relates to the alkylation of olefinic hydrocarbons with isoparaffin hydrocarbons in the presence of an alkylation catalyst mixture comprising hydrofluoric acid (HF) and, optionally, a volatility reducing additive. More particularly, the invention relates to the removal of HF from an alkylation catalyst mixture by contact with a gas stream comprising isoparaffins and/or olefins in a stripping column.
The use of catalytic alkylation processes to produce branched hydrocarbons having properties that are suitable for use as gasoline blending components is well known in the art. Generally, the alkylation of olefins by saturated hydrocarbons, such as isoparaffins, is accomplished by contacting the reactants with an acid catalyst to form a reaction mixture, settling the mixture to separate the catalyst from the hydrocarbons and further separating the alkylation reactor effluent, for example, by fractionation, to recover the separate product streams. Normally, the alkylation reactor effluent of the alkylation process contains hydrocarbons having five to sixteen carbon atoms per molecule, preferably seven to nine carbon atoms per molecule. In order to have the highest quality gasoline blending stock, it is preferred for the alkylate hydrocarbons formed in the alkylation process to be highly branched and contain seven to nine carbon atoms per molecule.
Recent efforts to improve conventional hydrogen fluoride catalyzed alkylation processes have resulted in the development of new catalyst compositions that contain hydrogen fluoride and a volatility reducing additive. These new catalyst compositions have been found to be quite effective as alkylation catalysts and provide many other favorable benefits.
Regeneration of an alkylation catalyst mixture containing HF, acid soluble oil (ASO), and, optionally, a volatility reducing additive generally includes stripping HF from the catalyst mixture using a combination of elevated temperatures and an isoparaffin stripping gas, for combination of the stripped HF with the alkylation catalyst mixture. The bottoms stream from such a stripper (commonly referred to as a re-run column) contains the ASO and, if present, the volatility reducing additive. Where a volatility reducing additive is used, the re-run column bottoms stream is then separated into an ASO stream and a volatility reducing additive stream, and the volatility reducing additive stream is combined with the alkylation catalyst. On occasion, in the operation of such a re-run column, adequate heating capacity and/or stripping gas (isoparaffin) is not available in order to adequately remove HF from the bottoms stream. Elevated levels of HF in the bottoms stream requires neutralization and a costly loss of such HF, and can cause less efficient separation of ASO from the volatility reducing additive. Therefore, development of an efficient process for reducing the concentration of HF in the bottoms stream of an isoparaffin re-run column used in an alkylation process would be a significant contribution to the art.
It is an object of the present invention to provide a novel method for regenerating an alkylation catalyst containing HF, ASO and, optionally, a volatility reducing additive.
It is a further object of this invention to provide an improved method for removing HF from a regenerable alkylation catalyst containing HF, ASO and, optionally, a volatility reducing additive.
A still further object of this invention is to provide a method for reducing the concentration of HF present in the bottoms stream of an alkylation process system re-run column.
A yet further object of this invention is to provide a method for increasing the ASO recovery from an alkylation process system re-run column bottoms stream.
The present invention is a method for regenerating an alkylation catalyst mixture used in an alkylation process system comprising the steps of:
alkylating a first olefin with a first isoparaffin in the presence of an alkylation catalyst mixture comprising HF in an alkylation reaction zone thereby producing an alkylate product and an ASO reaction by-product;
passing an alkylation reaction zone effluent comprising the alkylate product, the ASO reaction by-product and the alkylation catalyst mixture from the alkylation reaction zone to a separation zone for separating the alkylation reaction zone effluent into a hydrocarbon phase comprising the alkylate product, and an alkylation catalyst mixture phase comprising the alkylation catalyst mixture and the ASO reaction by-product;
passing at least a portion of the alkylation catalyst mixture phase to a re-run column for contact with an upwardly flowing gas stream comprising a second olefin and a second isoparaffin to provide a re-run column bottoms stream comprising at least a portion of the ASO reaction by-product, and a re-run column overhead stream comprising HF, at least a portion of the gas stream and an organic fluoride.
Other objects and advantages will become apparent from the detailed description and the appended claims.